An electrical power distribution system is generally composed of a distribution line onto which equipment is connected whose power is supplied by the distribution system, and which “load” the distribution system to a greater or lesser extent depending on the value of the impedance that they present. It also comprises means for producing the electrical power delivered together with control means that act on the electrical power production means in such a manner that the electrical power produced is, at any given moment, as adapted as possible to the load imposed by the equipment installed on the power supply line.
The distribution system is generally configured and dimensioned so that, in nominal operating mode and taking into account slow variations in load, it is able to deliver, with a certain safety margin, the electrical power demanded by the totality of the connected equipment. In other words, these means are dimensioned for delivering a given average power, while accepting to a certain extent variations around this average value of delivered power, which variations are preferably small and slow. For this reason, it is often necessary to insert, between the applied load and the distribution system, a device capable of detecting the variations in this load and of reacting to these variations by acting in such a manner as to limit their impact, or even by supplying the totality of the additional power demand using, for this purpose, an energy storage device.
In order to provide the power supply from an AC distribution system for high-power equipment, as illustrated in FIG. 1, a structure comprising a device commonly called a PFC, an acronym for the expression “Power Factor Corrector”, is generally inserted. This device, of structure known from elsewhere, carries out the conversion of the AC current supplied by the AC distribution system into DC current. This type of device mainly comprises AC-DC conversion means, together with means for the closed-loop control of the DC voltage produced to a given setpoint value which corresponds to the supply voltage required by the connected equipment. In this way, a variation in the load of this equipment normally causes an increase in the current produced by the PFC which then absorbs a higher power on the distribution system.
The PFC is generally associated with a set of means forming a feedback chain whose role is to detect the variations in load presented by the equipment connected to the distribution system, which variations in load result in a drop in the DC voltage delivered to the equipment. When such a voltage drop is detected, the means composing the feedback chain act on the PFC in such a manner that the latter delivers a DC current responding to the current demand induced by the variation in load.
One known drawback of the devices of the PFC type is that they necessarily have a relatively long reaction time, in order notably to preserve the quality of the primary AC distribution system (voltage dip and harmonics), which distribution system is generally powered by means incapable, by nature, of rapidly handling an increase in the power demand. The PFC therefore comprises a slow voltage feedback control loop, whose cutoff frequency is much lower than the frequency of the distribution system, so that it is able to absorb on the primary an AC current in phase with the voltage, and comprising the fewest possible harmonics.
The low bandwidth of the closed-loop control of the PFC therefore limits the quality of the regulation of the DC voltage when faced with rapid variations in load, and in particular in the case of a load of a pulsed nature. Thus, in order to respond to an abrupt variation in the load presented by the equipment connected to the distribution system, complementary means need to be provided capable of overcoming during a relatively long interval of time the incapacity of the PFC to deliver the necessary power.
These complementary means are generally means capable of storing and of returning electrical power, mainly banks of accumulators or capacitors. These energy storage means here are dimensioned so as to ensure a complementary provision of power during the interval of time necessary for the PFC to be able to handle the additional power demand from the equipment and to maintain a satisfactory power supply for the equipment despite the variation in load.
In practice, as illustrated in FIG. 1, such a structure is known which associates energy storage means with the PFC using a device of the chopper type. The chopper circuit here is designed to alternately adopt two states of operation: a first state in which it is configured for discharging the electrical power stored in the storage means on the DC line that supplies the equipment connected to the distribution system, and a second state in which it is configured for recharging storage means using the electrical current produced by the PFC.
According to this known embodiment, the passage from one state to the other is directly controlled by the state of operation of the PFC. Thus, when the PFC finds itself, at a given moment in time, incapable of producing the necessary power, the chopper is controlled in such a manner as to discharge the energy storage means such that the latter provide a complementary current on the power supply line which will be added to the current produced by the PFC in order to supply the equipment with the required power. Similarly, when the PFC is capable of supplying a power higher than the power demand, the chopper is controlled in such a manner as to recharge the energy storage means. The control of the chopper 16 is generally based on information directly supplied by the PFC, which indicates that the current supplied by the PFC is sufficient or otherwise in order to power the equipment correctly.
However, given that the process of regulation of the output power by the PFC is a slow process, an abrupt variation imposed on the load is only taken into account by the PFC after a relatively long lapse of time. Consequently, during a given lapse of time that follows the moment in time corresponding to an abrupt variation in the load, the PFC 11 shows no reaction such that, since the chopper 16 is not controlled so as to discharge the storage means, there occurs a deficit in the power supplied which results in a drop in the voltage delivered.
This known embodiment finally leads to a distribution system being obtained whose power exhibits an insufficient regulation, in particular when faced with abrupt and large variations in load, capable of having a significant effect on the operation of the equipment being powered.